Your questions answered: hydrogen fuel cell vehicles

The first hydrogen fuel cell vehicles are set to hit the market by the middle of the decade, with several major car manufacturers developing hydrogen-powered models and the UK already running a cross-industry trial programme to evaluate their usefulness.

For the latest in our series of technology Q&As, we asked for your questions on hydrogen vehicles to be answered by a panel of experts who kindly agreed to take part.

Thank you to all our readers you submitted questions. Providing answers are:

What advantages do hydrogen-powered vehicles have over battery electric vehicles given the current state of the two technologies?

(suggested by Don Isiko)

Hugo Spowers, Riversimple

The key advantages of fuel cell electric vehicles (FCEV) over battery electric vehicles (BEVs) are the range, refuelling time and, for vehicles with the range to which we have become accustomed, efficiency. Efficiency is tightly coupled to weight, and batteries are a heavy means of storing energy, so as the range for which a battery electric vehicle is designed goes up, the efficiency goes down, rapidly. There is also a recurrent argument that it makes more sense to use electricity to charge a BEV than electrolyse water to fuel a hydrogen car. This is very misleading in that almost all hydrogen comes from natural gas rather than from electrolysis and this process is 75% efficient, whereas the UK grid figure for electricity from natural gas, considered our cleanest form of fossil generated electricity, is 49%. However, BEVs and FCEVs should be seen as complementary. We need a mix of fuels and powertrains in the future, addressing different needs, rather than a versatile ‘one size fits all’ solution that does everything inefficiently; BEVs are great for short range applications but it makes no sense to drive from London to Edinburgh in one.

Hugo Spowers, Riversimple

How do the overall ‘well to wheel’ emissions of the latest hydrogen vehicles compare to those of diesel cars?

(suggested by Vince Carr)

Well to wheel performances of various fuels depends on very diverse supply and usage parameters. Let’s assume the comparison of usual diesel fuel (from refined oil) in a direct injection internal combustion engine (ICE) vs an FCEV: using hydrogen from the most familiar process (hot steam reforming), the FCEV would reduce CO2-equivalent emissions by about 30%, while hydrogen produced from renewable electricity via electrolysis would allow a reduction of well over 90%.

(More specific comparisons can be found using online tools such as this one.)

Gerard Planche, General Motors

General Motors expects to launch its HydroGen4 vehicle by 2016.

Would the incorporation of hydraulic drive increase the range of hydrogen vehicles by allowing less loading of the fuel cells during acceleration/deceleration? Is this something being used by or studied by manufacturers?

(suggested by James Stewart)

We have been developing a Network Electric platform at Riversimple that decouples constant and transient demands as you suggest - load levelling. This is absolutely essential for the commercialisation of FCEVs and it goes beyond merely increasing range; it also fundamentally changes the commercial viability of the fuel cell itself by reducing power requirement, as explained above. However, although we have looked at every possible solution for load levelling, we are not using hydraulic drives. This is because we are focused on overall system efficiency; as well as losses in primary elements in the system, every energy conversion process has losses, and so a coherent set of system components in the network, using a common energy vector, is usually more efficient. Using a combination of fuel cells, motors, super-capacitors and batteries allows us to use electricity throughout and maximise efficiency at the level of the whole system.

Hugo Spowers, Riversimple

What is the best method of hydrogen storage and why - compression, cryogenic, or metal hydride?

(suggested by Andy Gizara)

Dr Graham Cooley, ITM Power

Compressed gaseous hydrogen is the standard storage method used in vehicles by all major automotive OEM’s and is therefore widely used and understood. The pressure at which hydrogen is stored on board a road vehicle is 700 bar to ensure adequate energy can be accommodated on-board the vehicle so provide the range demanded by customers. Cryogenic used when large quantities of hydrogen need to be moved as it manages to pack even more hydrogen into a given volume. However, a complication with this method is that it requires a significant amount of energy to liquefy hydrogen because it needs to cooled down close to absolute zero in addition to being heavily compressed. Furthermore, some hydrogen losses are expected from transported liquid hydrogen stores due to boil off. Metal hydride can achieve high energy density and is a credible candidate for hydrogen storage where space is at a premium. It does, however, place restrictions on the rate at which the hydrogen can be introduced to the store and released. It also requires thermal management during the adsorption and desorption processes. At present, the lowest cost hydrogen storage method is compressed gas.

Dr Graham Cooley, ITM Power

Cryogenic storage is the most effective choice for large quantities, making fuelling station supply via trailer about ten times more efficient compared to 200 bar gaseous cylinders, for example. For smaller quantities - like the approximately 4 kg in a vehicle-mounted tank - 700 bar gaseous hydrogen is an agreed-upon industry standard, offering the best trade-off between energy density (vehicle range) and technical effort for compression. Other hydrogen storage options do exist, of course, but as we see it, they are currently only used for niche applications. Metal hydrides, for example, are used in a class of military submarines. In this special case, the weight of the MH storage unit is not as disadvantageous as it was in a car but is in fact an appreciated ballast for the boat.

Markus Bachmeier, Linde

ITM Power, Linde (BOC) and General Motors are part of the UK H2 Mobility trials.

What are your thoughts on the possibility of using hydrogen microbeads as fuel (an idea put forward by UK firm Cella Energy)?

(suggested by Brian Tucker)

Advances in hydrogen storage technologies are a good thing. However, it is considered unlikely that they will displace gaseous hydrogen storage in the medium term. Central issues associated with micro beads, for example, is the rate at which the hydrogen can be adsorbed and desorbed plus the logistics associated with getting ‘charged’ beads to the place where they are required and ‘spent’ beads to a location where they can be ‘recharged’. ITM believe the most effective hydrogen delivery mechanism is to generate on-site via an electrolyser fed by renewable power.

Dr Graham Cooley, ITM Power

What chance is there that a hydrogen distribution infrastructure could be used to fuel traditional internal combustion engines, thereby cutting emissions for a much lower cost, and why? Are any steps being taken towards this model?

(suggested by Peter Higgins)

Gerard Planche, General Motors

A traditional ICE needs to be modified to run on hydrogen. The relatively high cost of hydrogen storage cannot be avoided. A FCEV today already has twice the efficiency of a good diesel. And the ICE will produce more greenhouse gases using conventionally produced hydrogen than it would with gasoline! Naturally, emissions would be dramatically reduced with hydrogen produced from renewable sources, but will always remain above those of an FCEV. Moreover, the high temperature combustion in the cylinders creates nitrous oxides, not greenhouse gases but generators of smog and acid rain. Finally, the ICE would still be as noisy as when running on fossil fuels: noise is an underestimated environmental nuisance, particularly in cities. Some manufacturers have converted ICE models to run on hydrogen, but with the cost convergence of the various technologies in a relatively near future, the current advantage of that transitional and imperfect solution loses all its justification.

Gerard Planche, General Motors

How do you address the problem of hydrogen embrittlement (where metals become brittle following exposure to hydrogen)?

(suggested by Andy Gizara)

Hydrogen embrittlement only affects specific metals, principally high strength steels, and only where pressure is high, so the problem is completely avoided by using appropriate materials in high pressure sections of the system.

Hugo Spowers, Riversimple

Would it not be safer to generate the hydrogen from water on board a vehicle rather than store it in a tank (and have lower fuel costs)?

(suggested by Ken Wilks)

Hydrogen generated from water via electrolysis is the ideal fuel generation route as it permits green hydrogen production by accessing renewable power. There are two significant benefits to the hydrogen fuel being produced externally to the vehicle. The first is purely practical – the volume and weight of hydrogen generation equipment is such that incorporating it within a vehicle presents significant challenges. The second is the ability to separate the requirement for electrical power from the refuelling event, owners of BEVs dictate when the demand load is connected to the grid. With electrolytic hydrogen, it is the grid manager who decides when the load is added to generate the hydrogen gas, effectively this is a demand side managed load that helps to assimilate intermittent and varying sources of renewable energy.

Dr Graham Cooley, ITM Power

Riversimple’s Network Electric car is designed specifically for its fuel cell powertrain.

How does the safety of carrying hydrogen in a car compare to that of a petrol or diesel-powered vehicle and what measures have you introduced to ensure safety?

(suggested by The Engineer)

Hydrogen storage in a vehicle is safer than petrol or diesel for three reasons. First, the tank is much more robust than a conventional tank so is much less likely to be ruptured in an accident. Second, as a gaseous rather than a liquid fuel, no air is introduced in order to feed fuel to the prime mover, so no combustible mix of fuel and oxygen ever arises. And finally, if hydrogen does ever escape, it goes upstairs very quickly, rather than pooling under the car to incinerate it. Good vehicle design is able to maximise these advantages by protecting the tank in accidents. However, the facts alone are not enough and there is no doubt that there is a PR issue to be addressed whilst bringing hydrogen to market.

Hugo Spowers, Riversimple

By using hydrogen as an energy storage medium, are you not adding an unnecessary (and therefore inefficient) step in powering a vehicle? Why isn’t it better to use the electricitydirectly?

(suggested by Chris Wood)

Using electricity directly is more efficient indeed, but the very different driving and load profiles encountered in today’s traffic do not make a BEV the best solution to all mobility needs. Fast-charging of batteries has a negative impact on their useful life so that it will remain much longer to load a BEV than to refill a hydrogen car (hours vs minutes). Storing electricity in a battery requires much more weight and volume than under the form of liquid or high-pressure gaseous hydrogen. Hydrogen storage even starts to make inroads into applications heretofore dominated by batteries and where volume and mass are less of an issue - such as stationary applications. That signals that we reach a point of indifference in cost, reliability and convenience between the two storage technologies, which should be even more true in vehicle applications. The fact that the range of a BEV is directly proportional to the size and weight of its battery doesn’t make a BEV convenient for longer trips, nor a BEV with a high range - and therefore a heavy battery - would be efficient in day-to-day traffic. As a point of comparison: to drive 500km with one charge requires today a battery weighing close to a ton, whilst a 125kg hydrogen tank system can store enough energy (6kg of hydrogen) to do the job.

Gerard Planche, General Motors

Inside ITM Power’s mobile refuelling station.

How will airborne pollutants including other vehicle combustion emissions affect the performance of the fuel cells, specifically through catalyst poisoning?

(suggested by Ed Gummow)

The catalysts used in fuel cells can be subject to degradation if pollutants are introduced into the system. It is however possible to filter out conventional road pollution on the air intake. At an R&D level work continues towards the development of catalyst systems tolerant to such pollutants.

Dr Graham Cooley, ITM Power

What are your thoughts on developing offshore hydrogen farms that use wind turbines to electrolyse seawater and pumping or carrying the resulting hydrogen to shore? Have you got any plans to explore this option?

(suggested by Anonymous)

Markus Bachmeier, Linde

Storing fluctuating “green” electricity in hydrogen is a very interesting option indeed - in fact one of the most striking unique selling points of hydrogen altogether. It can be a substantial contribution to the so called energy turnaround - something that neither batteries nor pumped-storage plants would be able to accomplish. Currently, we are developing a wind-hydrogen project together with wind electricity provider Enertrag and oil multi TOTAL in Germany, near Berlin. In this project, our partner will generate hydrogen from water via electrolysis at a “multi-energy refuelling station” to be located at the new Berlin airport, currently under construction. Electricity comes from a nearby windpark. Linde is responsible for the design, installation and commissioning of the hydrogen refuelling that will supply passenger cars and buses with the renewable, zero-emission hydrogen. Of course, for a beginning, this is an onshore project, but provided results are as expected, the concept might well be applied to offshore windparks as well. We are not aware of electrolysers that can use seawater, so we would expect the electrolysers to be most probably located on-shore, and using hydrogen as a buffer storage in considerable dimensions will require large-scale storage facilities, e.g., underground caverns. But technically speaking, we don’t see any serious obstacles and will further explore the possibilities in this direction.

Readers' comments
(9)

Anonymous | 7 Dec 2012 6:23 pm

The big issues I see with hydrogen, as addressed above, include production, transport, and storage. But the downside is not fully discussed or realized. For production, it is most economic to think on mass scales, and currently NG reformation is by far the lowest cost at scale -so we are still relying on fossil fuels. Transportation of H2 is costly due to energy required to store H2 and the losses that occur along the way. Local production mitigates this but then we lose economies of scale on the production (meaning it is expensive to produce locally). On board H2 storage in 700psi tanks is reasonable, but in the very rare event that one tank explodes in an accident or from a defect, there will be very negative goodwill toward the car company. Many will not want this risk (however small). Gasoline can catch fire / explode, but the public is not accustomed to the shrapnel and mini-crater formed by a high pressure explosion.

Much effort has been put into the hydrogen fuel cell, so much so that it is ready for prime time... but the fuel I'm afraid is not.

My guess is the FC community will have to focus on modifying the FC to accept liquid H2 carrier fuels (methanol / ammonia etc). As a liquid, the energy density is higher, it is safer to transport, and easier to store. The downside is the added cost to convert the h2 to liquid, but this is old science and would lead to lower total costs compared to a gaseous H2 economy.

Many are working in this area already, and I would say that those who press ahead with the gaseous model may not survive in the end.

Nice to see these responses codified. Hydrogen suffers from misconceptions often repeated by those with a modicum of engineering knowledge but which is sadly outdated or inadequate. We as experts often forget to restate the basics.

ITM power seem as though they have an axe to grind regarding hydrogen micro beads from Cella Energy. Something as intrinsically safe as micro beads should be considered more carefully rather than dismissed as something for the long term.

There are companies offering hydrogen fuel cells as part of the domestic power supply. A good illustration can be found at the following url: http://www.actagroup.it/applications_home.asp

Anonymous | 3 Jan 2013 11:19 am

"Would it not be safer to generate the hydrogen from water on board a vehicle rather than store it in a tank (and have lower fuel costs)?"

I am surprised that the respondent did not raise the obvious issue of "where on the car would you store the energy to electrolyse the hydrogen, and why wouldn't you just use that energy to drive the vehicle"?

Any chance that you could put a link to my Petition for Hydrogen Fuelling Pints at Motorway Service Areas please.http://you.38degrees.org.uk/petitions/hydrogen-filling-points-at-all-motorway-service-areas?